Annunciator system



July 31, 1962 H. E. TELLEFSEN ETAL Re425,214

ANNUNCIATOR SYSTEM 5 Sheets-Sheet 1 Original Filed May 20, 1957 July 3l, 1962 H. E. TELLEFSEN ETAL ANNUNCIATOR SYSTEM Original Filed May 20, 1957 rRe. 25,214

s sheets-snaai s f'om eilig' 4pm/nc. Cinca/f5 United States Patent (')litrice Re. 25,214 Reissued July 31, 1962 25.214 ANNUNCIATOR SYSTEM Harold E. Tellefsen, Chicago, Richard L. White, Skokie, and Sergio Alessio, Chicago, Ill., assignors, by mesne assignments, to Isi, Incorporated, Los Angeles, Calif., a corporation of Delaware Original No. 2,931,018, dated Mar. 29, 1960, Ser. No. 660,137, May 20, 1957. Application for reissue Sept. 19, 1960, Ser. No. 57,092

13 Claims. (Cl. 340-213) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specilication; matter printed in italics indicates the additions made by reissue.

This invention relates to annunciator systems of the type wherein a visual alarm unit, such as a light unit, is provided for each variable to be monitored, and, when the variable becomes abnormal, the visual alarm unit provides an indication that the variable has just become abnormal. A manually operable acknowledgement control is provided which, when operated, changes the indication of the visual alarm unit to indicate that the alarm has been acknowledged by the operator. Usually, an audible alarm is also provided to attract the operators attention to a central control panel containing the visual alarm units associated with practically all of the variables to be monitored in the plant involved, sothat the operator can determine at a glance the condition of all of the variables.

Annunciator systems of the kind just described have heretofore been hydraulically or relay controlled systems. Obviously, it is quite important for annunciator systems to be reliable since, otherwise, they could not fulfill their intended purpose. Due to mechanical wea-r on relay contacts and of the various movable parts in hydraulic systems, the reliability of such annunciator systems left much to be desired.

It is, accordingly, one of the objects o-f the p-resent invention to provide an annunciator system operating, for the most part, with non-mechanical or static components, such as magnetic core units having opposite magnetic states which respectively are utilized to control the operation of the alarm units.

Another object of the present .invention is to provide an annunciator unit which operates electrical alarm units with static or nonmechanical control components, for the most part, and which therefore minimizes the nurnber of places in the system where sparking may occur, so that the system may be used in explosive atmospheres without providing extensive hermetically sealed housings for the control components in question.

A further object of the present invention is to provide an annunciator unit utilizing non-mechanical or static control components, particularly magnetic core units, comprising a minimum of components and at a minimum cost. A related object of the present invention is to provide annunciator units of magnetic core control units which may substantially duplicate the type of visual alarm unit sequences heretofore available in relay controlled annunciator units.

A still furhter object of the present invention is to provide an annunicator system which is of substantially simpler construction and is less expensive than prior annunciator units of a similar or less degree of reliability and providing a similar visual alarm sequence.

An `over-all object of the present invention is to provide an annunciator unit accomplishing all of the various above-mentioned objects.

In accordance with a preferred form of the invention, the basic annunciator alarm sequence is obtained through the use of only two magnetic core units, each having an input and an output winding wound about a core of magnetic material having a rectangular hysteresis characteristic, to provide sharply-delined opposite magnetic states of staturation. In magnetic cores of this type, if a main signal source is connected in series with an output winding of one of the core units and with a load device, which may comprise the input winding of the other core unit, the output winding of the first-mentioned core acts like a high impedance when the signal source is driving the core between its opposite states of saturation, resulting in a relatively small current or voltage in the load device or input winding of the second-mentioned core unit. This may represent a so called no-signal output condition of the core unit. If the signal from the signal source is operable to maintain merely the state of saturtaion of the core, so that the core is not reset thereby to opposite states of saturation, then the output winding actslike a relatively small impedance, and a relatively large voltage or signal appears in the load device. This may be referred to as a signal output condition of the core unit. The core unit thus acts like a gate circuit which is closed when the core is being driven between its opposite states of saturation and which is open when its state of saturation is being maintained. The relatively large signal occurring in the output circuit of the iirst core unit could be utilized to trigger the secondmentioned core unit, constituting the abovementioned load device, to an opposite state of magnetic saturation.

It can thus be seen that if a control signal source is connected across the input Winding of the rst-mentioned core unit, which signal source provides spaced-apart driving pulses of a polarity which drives or sets the firstmentioned core only from a reference to an opposite state of saturation during periods occurring between the application of similar drive pulses provided by said firstmentioned main signal source which pulses reset the core to its reference state of saturation, a no-signal output condition at the output of the first core unit Will be provided. Now, if the input winding of the second core unit is connected as the load for the first core unit and the output winding of the second core unit is connected to a second main signal source producing spaced-apart resetting drive pulses which occur between the drive pulses of the first main signal source, the no-silgnal output condition of the iirst core unit, which is the control signal input condition of the second core unit, will enable the second main signal source to maintain the state of saturation of the second core unit and thus provide a signal output condition therefor. The signal output of the second core unit could be the abovementioned control signal source of the first core unit, if the output of the second core unit is fed to the input winding of the iirst core unit. In such case, a bistable circuit is provided wherein the signal output condition of either core unit controls the signal output condition of the other core unit. Moreover, each core unit is connected as a not gate circuit, meaning that a signal output condition is present if a no-signal condition exists at the core input and a no-signal output condition is present if a signal condition exists at the core unit input.

An annunciator circuit is formed with the above-mentioned bistable gate circuit by connecting a first visual alann means in the output circuit of one of the core units and providing a condition-responsive control means, such as a normally open or normally closed set of field contacts, lwhich may be a thermocouple controlled set of contacts where temperature variables are involved, which exercises control over the output condition of said one core unit, or the elfect of an output condition of the core unit on the visual alarm means. The field contacts are also preferably connected to a second visual alarm means which is controlled directly by the field contacts, independently of the core units. An acknowledgement witch is provided which when momentarily depressed i'g'g'ersthe core unit controlling the rst visual alarm neans to a no-signal output condition which de-enerizes the first visual alarm means without affecting the econd visual alarm means. The interconnection of the ore units is such that the no-s'ignal condition of the itte'r core unit isl maintained even though the acknowldgement lswitch is released. Between the co-nditions of 1e two visual alarm 'means,` the operator can tell `/hether the variable yinvolved is normal or abnormal, nd, if abnormal, whether it has been acknowledged by 1e operator.

Other features of the invention relate to the particular rrangement of cir-cuit componentsA usedY in conjunction llith-the various core units to provide for maximum rea'bility and'minimum cost. An annunciator circuit contructed in accordance with the present invention can e' made to sell for a substantially lower price than relay nnunciator units' now `'available on the market. In adition to the Ylower cost, the circuit offers substantially reater reliability than relay annunciator circuits and ther types of annunciator circuits heretofore utilized.

Other objects, advantages and features of the invenon will become `apparent by making reference to the pecification to' follow, the claims and the drawings 'hereinz vfFIG; l is a simplified box diagram of an annunci-ator ircuit constructed in accordance ywith the present invenon;

'FIG 2, is a detailed circuit diagram showing one form f the present invention utilized with normally open field oi'ltaicts;N

FIG. 3 shows various current and voltage waveforms t different parts of the circuit of FIG. 2, under various onditionsofV operation o-f the annunciator circui-t; Y

FIG. 4 shows a sample hysteresis curve of the core laterial usedi'n the core units of the annunciator circuit; yFIGQSS a table of the 'various operating conditions f the Vannuc'iator circuit of FIG. 2;

FIG. y'shows 'a method of mounting the alarm lights that a standard flashing sequence is obtained;l

FIG. 7 shows 'a form of the present invention operating ith normally 4closed field contacts and utilizing transtors for directlyl controllingthe energization of the a'rm lights;

FIG. 8 shows another form of the present invention 'ranged to be operated :with normally closed field conctS;

FIG. 9 shows a still fur-ther and preferred form of the usic invention; FIGfl'shows the current and voltage waveforms in Lrious' parts ofthe annunciator circuit in FIG. 9, durg theV various phases o-f operation thereof; and

FIGfll is a table illustra-ting the various operating contionsof the annunciation circuit of FIG. 9. Refer :now to FIG. l whichy illustrates an annunciator rparatus in' box diagram form constructed in accordance Lththe present invention. ay include the 'basic components usually found in anlnciator systems, including 'a suitable variable condition spons'ivedevice, such as eld contacts 2 which have posite 'positions of operation representing respectively `rrnal `and abnormal conditions of the variable being onitored, visual. alarm'means which may comprise iiteiandred alarm light means 4 and 4' including reectively' a White light W and a red light yR, and an aclowledgement switch 8. Although a separate two-light stem is shown, Vit will be shown later on that an apij'ent one-Iig'ht'systemrmay also be formed byucombing the two lights Rand W in a manner to be explained. In -aftwo-light system, when the field contacts are p tted to their Aalarm indicating positions, the annunltor apparatus may energizeV both light means so that e white light Wgand the red light Rwill'both be lit ightly. Provision is usually made for energizing an The annunicator apparatusA audible alarm such as a horn 9. Light sources W and R are normally mounted on a comm-on panel with a large number of other lights associated with other variables. In such case, it may be desirable to provide a flashing light indication for, say, the red light source R, to attract the operator to the particular part of the panel where the lights in question are located. The red light means I4', may, in such case, include flasher apparatus for flashing the red light source R. When the acknowledgement switch 8 is` momentarily depressed, the visual alarm indica-ting means are changed to indicate an acknowledged alarm condition, assur-ing tha-t the variable involved is still abnormal. In the embodiment being illustrated, the acknowledged alarm condition may be shown by extinguishing the red light R, leaving only the white light source W brightly lit. In the one light visual alarm sequence, an initial alarm indication could be identified by a flashing light and an acknowledged alarm condition could be indicated by a steady light. When the Variable being monitored returns `to normal, the alarm lights are extinguished.

In accordance with the preferred form of the present invention, the field contacts and the acknowledgement switch are associated with magnetic core controlk circuits, generally indicated by reference numerals 10 and 10', arranged as not gate circuits. The magnetic core not gate circuit 10 is fed from a main signal source E1 connected to a main signal input terminal 16. Ap-

preciable signals from the main signal source E1 will.

appear at a signal output terminall 18 of the gate circuit 10 in the absence of control signals at a control signal input terminal 20, to be referred to as a not input. terminal. When no signal appears at the not input ter.- minal 20, thena signal output appears at the signal output terminal 1S originatingin the main signal source E1.

The signal output terminal 18 of the not gate circuit 10 is connectedvia a line 21 to the not input terminal 20 of the other not gate circuit 10. The gate circuit`r 10' h as -a mainsignal input terminal 165 fed by a second mainA signall source E2. Appreciable signals from the main signal source E2 appear at a signal output terminal `18 of the gate circuit 10i in the absence of a signal input condition at the not input terminal 20" thereof. Conversely, when a signal condition appears at.the.sig nal input terminal 20", a no-signal output condition will appear at the signal output terminal 18. ofthe gate` circuit 10. The signal output terminal 18T of the gate circuit 10 is connected via a linel 23 ,tothe not signal input terminalllofnfthe first gate circuit 10, so that a bistable arrangement of gate circuits are provi-ded, wherein the output conditions of each lgate circuit controls the outputconditions of the other gatey circuit. In such case, if one of the gate circuits has a signal output condition, the signals fed therefrom to the not control` input terminal ofthe other gate circuit will insure a no-signal` output condition of the latter gateAcir-cuit. The 11o-signal condition of the latter gate circuit will insure a signal output condition of the former gate circuit. The signal.

output conditions ofthe two gate circuits may be reversedl'by any means which Ieven4 momentarily changes the signal outputcondition of one of the gate circuits, since this will then result in a reversal of the output. condition of the following gate circuit.

Inl the two-light system illustrated, the ywhite light means 4,1may comprise a source of` voltage, not shown, which is connectedl to the white light Wothrough the field contacts 2, in the case of `normally openfeld contacts. In the case of normallyfclosed field contacts, the field contacts mayy shuntvthe power'source Yfrom the white light source W. Alternatively, field contacts may control a suitable power or current amplifier, unit such as a transistor current amplifier, which in turn directly controls the energized lstate of the whitelight source W. Each of these variations will'beY described hereinafter. sufnce it to say, that the white light means tis direcny responsive to the position of the field contacts, and is independent of the output condition of the gate circuit or 10'. The red light means 4', on the other hand, may be controlled solely from the output of the gate circuit 10', or it may be controlled .both by the field contacts 2 and the output of the gate circuit 10", depending upon the particular design of the circuit in question. In any event, when the field contacts 2 are operated to ltheir alarm indicating position, output signals are fed from` the signal output terminal 18 of the gate circuit 10 to the red iight means 4', which cause the red light R to burn brightly, either in a steady-on or ashing condition, depending upon the particular desires of the circuit designer. rIhe initial alarm condition of the visual alarm means in the present example, would be that both the white and the red lights are burning brightly.

When the acknowledgement switch 8 is momentarily depressed, an inhibit signal source 32 is coupled to an inhibit signal input terminal 27. The inhibit signal appearing at the signal input terminal 27 effectively cancels out the elect of the signals fed to the signal input terminal from the output of the gate circuit 12, so that, momentarily at least, the circuit acts as if no signal appeared at the signal input terminal 20. This creates a signal output condition at the signal output terminal 18 of the gate circuit 10. Since the signal output condition now appears at the not signal input terminal 20" of the gate circuit 10', a no-signal output condition then appears at the signal output terminal 18 thereof. In such case, release of the acknowledgement switch 8 would not result in the reversion of the gate circuit 10 to a no-signal output condition because the not signal input at the input terminal 20 has now disappeared. The states of operation of the gate circuits 10- and 10" have thus been reversed, resulting in the cessation of output signals fed to the red light means 4 from the output of the gate circuit 10. The red light source R will then be de-energized. An acknowledged alarm state of the alarm lights will then be represented by the white light sour-ce W burning brightly and the red light source R extinguished. The white light source W is burning brightly because the field contacts 2 are still in an abnormal condition indicating position. When the variable being monitored returns to normal, the field contacts 2 will revert to their normal indicating position and the White light source W will become extinguished.

Refer now to the schematic diagram of FIG. 2 which shows one form of annunciator circuit used with normally open field contacts. For the most part, the gate circuits in this and the other illustrated specific embodiments of the invention are identical, and corresponding elements will be similarly numbered, except perhaps for the addition of a prime following the reference number of a particular component. Practically all the components utilized exclusively for monitoring each variable are contained preferably in a pair of standard identical plug-in units forming the respective not gate circuits 10 and 10'. The various signal input and output terminals previously described in connection with the box diagram of FIG. l may be the prongs of respective male connectors at the bottoms of plug-in units, which connectors fit within female connectors secured to a common chassis or mounting rb-ase, not shown. The chassis may carry or are connected to respective power busses carrying the above-mentioned signal voltages. These busses or the generators connected `thereto are thus the voltage sources E1 and E2 previously referred to. The busses make connection with the plug-in units through said male and female connectors. Voltage sources E1 and E2 may be any suitable alternating voltage sources providing pulses of sinusoidal or other shape, alternating in polarity. The alternating pulses of these sources are coincident but are of opposite phase or polarity, as shown by the exemplary sinusoidal voltage waveforms of FIGS.

3a and 3b. The positive pulses of these voltage source as will be explained, perform core driving functions an will be referred to as drive pulses, while the negatit pulses thereof perform current inhibiting functions t be explained. A frequency or positive pulse repetitie rate of kc. is desirable since it enables the use t relatively small core units.

Each of the plug-in units 10 or 10 has a magnetic co1 unit 37 or 37 which comprises a ring core 37a or 37; made of a material having a generally rectangular shape hysteresis curve shown in FIG. 4. The opposite saturate states of the core are represented by parallel horizontz curve segments S and S' spaced evenly below and above zero ux line L1, and the unsaturated conditions of th core are represented by the steep segment lines US an US similarly located on opposite sides of a zero mag netornotive force (M.M.F.) or ampere turns line L1 Each core 37a or 37a' has an input winding 37b or 37h and an output winding 37e or 37o. Most preferably, th output winding has a substantially greater number o turns than the input winding. For a core having kne points x-2 and x-3 located respectively two and thre units from the Zero line L1, a step-u] turns ratio of one to five was found highly satisfactory Such a step-up ratio insures reliable operation of the cir cuit, without requiring external biasing means. In suc] case the no-signal condition of a core unit would drive it load -core only to a point x-2' far below the near knel x-2 of the hysteresis curve,

A resistor 41 or 41 and a rectifier 39 or 39" are con nected in series between the upper end of the input wind ing 37b or 37b and a not control signal input plug-i1 terminal 20 or 20 of the gate circuits 10 or 10'. Th: bottom end of the input winding 37b or 37b is connecte( through a current limiting resistor 43 or 43' to a plug-i1 connector terminal 44 or 44. Plug-in terminal 44 is connected directly to ground through the socket terminal o: the associated female connector, not shown, and the other corresponding terminal 44 is connected to ground througl' a normally open set of condition-responsive field contactf 2. The junction of the dropping resistor 43 or 43 with the bottom end of the input winding 37b or 37b' is connected to the inhibit signal input plug-in terminal 27 o1 27 of the plug-in unit 10 or 10' through rectiiiers 45 o1 45. In the embodiment of the invention shown in FIG. 2, the inhibit signal input terminal 27' of the plug-in unit 10 is not used, but the inhibit signal input plug-in terminal 27 of the plug-in unit 10 is connected to an acknowledgement bus 8 to which the inhibit signal input terminals of all of the plug-in units 10 associated with other variables are connected. Pushbutton switch 8- is connected between the bus 8' and an inhibit signal source 32 which is connected to ground. The inhibit signal source, as will appear, may actually be the power bus associated with the signal source E2.

A signal input plug-in terminal 16 associated with the plug-in unit 10 is connected to the power bus associated with main signal source E1. The plug-in unit 10 has a signal output plug-in terminal 18 connected via the line 21 and the female connector of plug-in unit 10' to the not signal input plug-in terminal 20 of the plug-in unit 10. The plug-in unit 10 has a signal output plug-in terminal 1'8 which is connected via the associated female connector and line 23 to the not" signal input plug-in terminal 20 of the plug-in unit 10.

The white light means 4 comprises a circuit including a white light W and a suitable source of driving voltage 50 connected in series with one another across the eld contacts 2. Closure of the field contacts 2 will, therefore, energize the white light W and opening of the field contacts will de-energize the white light W.

The right light means 4 is a circuit including a rectifier 52 connected through the female connector of plug-in unit 10' to the signal output plug-in terminal 18' of the plug-in unit 10. A suitable asher unit 53 and a red t R are connected in sries between the rectifier SI2 the ungro-unded side of the Ilield contacts 2. The her unit 53 may be -any one of a number of well known ber units. It may comprise a snap-action bimetailic nent, or it lmay comprise a small motor energized by output of the core unit 37 or externally energized ch motor drives a cam which alternately opens and ;es a contact in the line in series with the red light R. The operation of the circuit of FIG. 2 may be explained ollows. When the field contacts 2 are open, the enrgizing circuit for the white light W and the input cirassociated with the input winding 37b of the right ld core unit 37' lare open, so that no current can How vhe input winding 37b. The energizing source 50 is so arized that the rectifier 39 in series with the input :ding 37b' blocks `any current liovv therefrom. The rgization circuit for the red light R is also interrupted the open lield contacts 2, so that the red light R is energized. The main signal voltage source E2 connected in series h the output Winding 37e of the core unit 37 feeds rent through a path including signal input terminal output win-ding 37e', feedback line 23, not signalinterminal 20, rectifier 39, current-limiting resistor 41, ut winding 37b of the core unit 37, input load resistor and the terminal 44 connected to ground. The recti- 39 is polarized to block current flow resultingfrorn the gative pulses of the output of Ithe alternating main sigsource E2. The positive or drive pulses of the signal .rce E2 are in a direction to drive the core 37a' of the e unit 37 into the reference state of saturation repreted by the curve segment S in FIG. 4, if the core is not :ady in such state, or to maintain such state of satura- 1 if the core is already in thisstate of saturation. Betse the energization circuit of the input winding 37b lorrnally open, the core 37a' will be continuously mainied in the reference state of saturation. In such case, output winding acts like a practically zeroY impedance llarge positive signal pulsations Io-2 (FIG. 3c) iiow a result of the drive pulses from signal source E2 in the ut winding 37a of the rst core unit 37. Gate circuit -is thus normally open. The impedance in the aforentioned current path iis such that there is sufiicient :rgy in each relatively large curr-ent pulsation passing ough the output Winding 37e' of the core unit 37 to input winding 37b or the core unit 37 that the core of 1 latter unit will be driven from poin-t-x-l oflits `refer- :e state of saturation, represented by the curved seg- `nt S in FIG. 4, to the knee point x3 of its opposite te of saturation represented by thecurved segment S.v

ien the current pulsation ends, the-state of operation of core 37a 4is represented by point x-4.

[he output winding 37C of the first core unit 37 is in oop circuit including main voltage source E1, rectifier resistor 41', input winding 37b of the second core it 37', resistor 43- and the iield contacts 2. The recti- 39 is arranged to pass the positive pulses of signal Lrce E1, which occur one-half cycle after the positive ve pulses of signal source E2. The negative pulses of nal source E1 inhibit or cancel out the effect of the l-ses induced into the'output Winding 37e of the first re unit 37 by the driving of the iirst core 37a from the lerence state of saturation S`to the second or oppositeV te of saturation S' (FIG. 4) by the drive pulses in-input nding 37b.

When the field contacts 2 `are open, no current can w in the output winding 37e and thus each subsequent rren-t pulsationliowing through input winding 37b il maintain the core 37a in its reference ,state of saturan S. When `an abnormal condition of the variable ing monitored exists, iield contacts 2 close to complete erg'zing current paths for the red Iand White light R and and for the loop circuit including the output winding cand the input winding 37b'. The red light R will sh due to the asher 53 and the white light W will be a steady bright light. A horn, not shown, may also be sounded. Then, the active or positive pulses from signal' source E1 are operative to drive the core 37a from its opposite state of saturation just to the knee point x-S on the curve segment. S representing the reference state of saturation. However, thisl will not change the signal output condition of the second core 37a because during the resetting of the iirst core 37a to its reference state of saturation, its output winding 37e with its large number of tu-rns rel-ative to the input windings 37b' acts like a 'large impedance Vwhich limits current flow to the small or no-signal output condition 'represented by the relatively small pulses Io-l shown in FIG. 3d. These small current pulsations Io-1 passing through the input Winding 37b of the second corefunit 37 are inv a direction tending to driye the second core 37a from its operating point x-l on the reference state of saturation curved segment Sy toward the opposite state of saturation. However, the

small current passing through a srnal'lA number of turns in the input Winding 37b will.' be insuiiicient to reach anywhere near even the nearest knee point x-2. The small current pulsations passing through the large number of.

turns in the output winding 37e will reset theV core 37a and the signal sources E1 and E2 will continue to set and reset the core 37a during. alternate half cycles untill the acknowledgement pushbutton 8 is momentarily depressed. The gate circuit or plugainunit 10 acts now like a closed gate andthe gate circuit. of plug-in unit 10. isstill` acting as an open gate providing an output signal condition.

which energizesl the redlightf R'.

If the above-mentioned small current pulsations lIo-l were to drive the core 37a into itsunsaturated. state, yet

to an insuiiicient degree to completely reverse the state of saturation of the core, diiiiculty would probably be encountered because the core would'then be sety to another state of saturation represented Iby the horizontal dotted line curved segment S-1. During the next hal-f cycle, when the drive pulse of the main signal source E2 drives the core to the reference state of saturation S, a current pulsation will be generated which has'insuicient energy to trigger the core unit 37a, which is the desired condition of operation or' the circuit. An inversion of the operations of the two gate circuits 10 and 1i)y will result, whichwill completely destroy the -proper operation of the :annunciator unit. So, it is important that the relatively small or no-signal current pulsations-not drive the core 37a beyond the nearest knee point x-2.

In the example now being illustrated, closure of the eld contacts 2 does not iactually disturb `the outputcon-V ditions of the not gate circuit 1()'vl It merely completed the paths of current iiow to the lights.

attention would be iattracted lto la central control panel' containing the lights W and R, either through the sounding of an audible alarm, not shown in FIG. 2, or by the rlashing of the red light R. The operator then momen- V tarily depresses the acknowledgement'pushbutton 8used` in common with a'll of the annunciator circuits (each circuit comprises a pair of plug-ins 1l]I `and'10 and associated lights) of the annunciator system. Depression of the pushbutton feeds the inhibit signal source 32 to the acknowledgement bus 8' and momentarily inhibits Ithe not signal input of the 4iirst -gate circuit 10 of beach annunciator circuit. The inhibit signal may have the same phase and wave shape as the output ofV the main signal source E2 and may thus be represented by the waveform sho-wn in FIG. 3b. The negative going pulsa- In accordance with a broader aspect of the invention, however, as will= tions thereof are blocked by the rectifier 45. Since theactive or positive going pulsations of lthe output of the inhibit signal source 32 are in phase with the corresponding drive pulsations fed to the not input terminal 20 from the output of lthe second gate circuit and these signals are applied to opposite ends of the input winding 37b, no current ows in the input winding 37b. The current-limiting resistor 41 connected between the upper end of the input winding 37b and the rectifier 39 serves the purpose of minimizing current flow due to any slight variations in the amplitude of the output of the control signal source 32 and the main signal source E2. When current flow is inhibited in the input winding 37b, the core 37a is not driven from its reference state of saturation S to its opposite state rof saturation S', so that the next occurring resetting pulsation vfed to the `output winding 37e -from the main signal source E1 will be in a direction to merely maintain the state of saturation of the core 37 a in the state S. As above explained, in such case the output winding 37o will act as a substantially zero impedance, so that a relatively large current pulsation will flow at such Itime through the rectifier 39', current-limiting resistor 49', input winding 37b', input resistor `43' and the field contacts 2 extending to ground. This large current pulsation represents a signal output condit-ion of the first gate circuit 10 which Vis now open, and are represented by a pulsation Ilo-1 shown in FIG. 3f. This large current owing through the input Winding 37b will set the second core 37a from its reference state of saturation S to its opposite state of saturation S in the same way that the large current pulsat-ions from the output circuit of the gate circuit 10 set the first core 37a from its reference state of saturation C to its opposite state of saturation S. One-half cycle following each such setting of the mag'- netic core 37a to its opposite state of saturation, a drive pulse of the main signal source E2 causes a resetting current to flow in the large number of turns of the output winding 57C', a resetting current or' relatively small magnitude because of the large impedance offered by the large number of turns of the output winding 37e', so that the current output of the core unit 37 may then be represented by a pulsation of the waveform IIo-Z shown in FIG. 3e. The gate 10 is now closed. This small current flowing through the small number of turns in lthe input winding 37b of the iirst core 37a will be insuf'iicient to drive the core into its unsaturated state, and certainly to its opposite state of saturation S', so that the saturation of the core 37 a is maintained by the active pulses generated by the main signal source E1. The voltage sources E1 and E2 will co-ntinue to set and reset the second core 37a', resulting in a maintenance of :a no-signal output condition thereat, and signal so-urce E1 continues to maintain the state of saturation of the core 37a resulting in a signal output condition thereat.

Since relatively little output appears at the signal output terminal 18' of the second core unit 37', insufiicient power is available to operate the red light R even though lthe field contacts 2 are still closed. Thus, in the acknowledged state of operation of the annunciator unit, while an abnormal variable still exists the white light W will burn brightly and the red light R will be extinguished.

As core 37a is triggered back and forth between the opposite states of saturation by the drive current pulses from signal sources E1 and E2 flowing respectively through input and output windings 37b and 3l'7c, voltage pulses are respectively induced in the windings 37C and 37b' which are polarized to produce current pulses which can pass through rectifier 39 and 39. Flow of such current pulses could adversely affect the operation of the circuit. The negative pulses of the main signal source E1 or E2 which is connected to the winding into which the unwanted voltage pulse is induced will oppose and cancel out -the effect of these unwanted induced voltage pulses.

When the variable being monitored returns to normal,

the field contacts 2 will open thereby disconnecting the input winding 37b of the second core unit 37 from ground. This will eiectively interrupt the dlow of setting current for the core 37a', so that the next drive pulse .generated by the main signal source E2 will maintain the state of saturation of the core 37a', resulting in a signal output condition of the core, `for reasonsV apparent from the explanation ofthe circuit operation above explained. This, in turn, operates to provide large signal current pulsations represented by :the waveform of FIG. 3c which will set the first core 37a to change the signal output condition thereof to a no-signal output condition. Opening of the eld contacts 2 will, of course, extinguish the white light W.

FIG. 5 is a chart which illustrates the core and output conditions of the annunciator circuit for the various types of operation of :the annunciator unit.

The annunciator light sequence just described can be changed to an annunciator sequence appearing like a conventional one-light flashing system by the simple expedient of mounting the white an-d red light bulbs W and R behind a common light-diffusing panel, such as panel P shown in FIG. 6. With this arrangement, it can be readily seen that during initial alarm operation, a ilashing light will appear on the outside of the lightdiffusing panel -P due to the ilashing red light R. After acknowledgement, the light will change to a steady indication because the red light R will be extinguished. In this case, the representations of red and white mean nothing since the ultimate color of light seen by the viewer is determined primarily by the color of the light-diffusing panel P.

When the iield contacts are located a substantial dis- -tance from the annunciator equipment and large load currents from the lights R and W pass therethrough, -a significant voltage drop may appear in the long lines extending to the field contacts. This voltage drop may, in some cases, aiect the reliability of operation of the circuit because this 4voltage represents a biasing voltage which opposes the si-gnal fed to the no input terminal 20 of the second plug-in unit 10', and therefore could render the circuit inoperable for its intended function. This situation can be avoided by replacing the red and white lights R and W by input circuits to current or power amplifiers. This type of circuit operation will now be described in connection with the embodiment of the Iinvention shown in FIG. 7, where normally closed field contacts are utilized.

In the embodiment of iFIG. 7, the identical plug-ins 10 and 10 are utilized which were just described in connection with the circuit diagram of tFIG. 2. The connections and functions of the irst plug-in unit 10 are identical to the connections and functions previously described in connection with FIG. 2. The arrangement of Ithe output circuit of the second plug-in 10 controlling the energization of the red light R is somewhat modied, however. This circuit includes the above-mentioned rectiiier 52 in series with a pair of resistors 56 and 58 connected to ground. The normally closed field contacts 2 are connected between ground and the junction point between resistors 56 and 58. This junction point is also connected to a base electrode `62 of a conventional transistor 63 of the so called NPN type. The collertor els-C- trode 616 of the transistor is connected through the red light R `to the positive terminal of a source of direct current voltage S0 whose negative terminal is grounded. The emitter electrode 64 is grounded. In a transistor amplifier of this type, when the base electrode is grounded, ilow of current through the load of the transistor is cut off. When a positive voltage of proper amplitude is applied to the base electrode, the transistor conducts. The direction of signal current flow in the output circuit of the gate circuit 10 is in a direction to apply a positive vo-ltage between the base electrode and ground, which the transistor connection shown will result in the flow current in' the output circuit of the transistor.`

The white li'ght circuit is` also controlled by a transisr amplifierf circuit. A resistor 82 is connected froml e ungrounded end of the field contacts 2 to the base ectrode 84 of a transistor 86 of the NPN type. The nitt'er electrode 88 of the transistor 36 is connected to oundf andthe collector electrode 90 is connected to hite light W which connects with the positive termi- Ll of aV direct current voltage source 50. A resistor f is connected between positive terminal of the voltage urce 50 and the end of the resistor 82 nearest the sld cont-acts. WithA this arrangement, closure of the :ld contacts will ground the base electrode `84 and erefore render the load circuit of the ltransistor non- `'nductive When the field contacts are open, the posiie voltage is suppliedV to the base electrode through the sistor 89` toinitiate current flow in the output circuit the transistor, Athereby turning on the white light W. When' the acknowledgement button 8 ismomentarily pressed, for reasons above explained, this changes the gnal' output condition of the gate circuit 10 to a no- ;nal output condition. In such case, since little or no rrent iiows through the resistor 58 connected to the .se electrode of* the transistor 63, the base electrode be- -mes effectively grounded which terminates current w in the load circuit of the transistor 63, thereby eX- lguishing the redv light R. The white light will coniue'to be lighted until the field contacts close. Then e, baseA electrode 84 will be grounded to render the load 'cuitthereof non-conductive.

The embodiment of FIG. 7 also illustrates the manner `which acornmon audible alarm in the form ofa horn may be utilized in conjunction with a' large numberv annunciator units similar to that just described. As

eviousl'yv indicated, each variable being monitored will ,ve' its` own annunciator circuit. It would be economi-Y lly unfeasible` to provide a separate horn for each nunciator unit. FIG. 7 shows a circuit wherein a igle horn 9 may be utilized in conjunction with any mb'er of annunciator uni-ts. The horn 9 is associated th a transistor 92 of the so called PNP type. The rn 9vis'c-onnected between Athe collector electrode 94 d ground.. A source of positive potential 50 is concted between the emitter electrode 96 and ground. t can be appreciated that all of the voltage sources i," 50' and 50" may be the' same power supply and uld, in effect, be a rectified A.C. voltage.) The base :ctr'ode 98` is connected in circuit with each o-f the nulnciator units to be utilized. In the transistor circuit W'b'eing described, ground or negative potential aped'to the base electrode 96 willrenderthe transistor` .tput circuit' conductive `and a positive potential Will nder the output circuit non-conductive. Normally, a sitivev voltage appearson the base electrode 98 beuse'ot the connection of the base electrode to the posi- 'eterminalof the voltage source Sti" through a. resisr- 99.Y The -connection between=the base electrode 98 dii each ofthe annunci-ator units includes respective :tifie'rsv 100, 100', 100, etc. in series with respective iistors 102,- 1025, 1025', etc., extending respectively to a-c'ollectorelectrode 65, etc., associated with the'trantor controllingthe energization of the respective red ht Rthereof. VThe collector electrode'66 of each of :transistor circuits controlling the associated red light effectively grounded-when the transistor is in its concting state. Therefore, when the-red light of any annicatonunit isf initially turned on, a ground potential ll beconnected through the associated resistors 102, 2', or'102, etc., and the associated rectifier 100, or. 10W', etc. to the base electrode-98 of the horn ntrolling transistor 92. The various rectifiers 100, 0', 100, isolate the various annunciator units from 'e another.'

Refer now to FIG. 8 `which shows another form of the FIG. 8, for purposes of simplicity. The connections made to the right hand gate -circuit 10" in the embodiment of FIG. S, however, are diierent from that shown in FIG'. 2. In FIG. 8 the input resistor 43" connected to the bottom of the input winding of the core unit 37 is con`- nected directly to ground instead of the field contacts. Also, the end of the red light R remote from the signal output terminal 18 is connected to ground instead of to the field contacts as is the end of the white light remote from voltage source 50. A connection is made from a plug-in terminal 42" connected at the juncture between the current-limiting resistor 41" andthe upper end of the input winding of the core unit 3 7', through a rectifier 103 to the ungrounded end of the normally closed field contacts 2, so that all drive input signals'to the input of the core unit 37 are grounded through the .rectifier 103 andthe ield'contacts 2 when the latter are' closed. This will assure a no-signal input condition' to the core unit 37 during normal operation of' the"system-being monitored. Both the red and white lights are similarly bypassed during the closed condition of theY field contacts by respective rectiiiers 104 and 105 connected between the ungrounded ends of `the white and red light bulbs W and R and the ungrounded endofv the field` contacts 2-. It can thus' be seen that, when the field contacts 2 open, the red and white lights are turned on and the shunt circuit across the input: winding-of the core unit 37 is opened, to prepare the core for operation bysignal pulses from the other gate circuit 1.0', when the acknowledgement pu'shbutton associated there? with islmomentarily depressed by the operator. The circuit of FIG; 8 in all other respects operates likeI the circuit of FIG. 2.

Refer now toFIGS; 9 to ll which relate to a substantially modified form of the invention. In the embodiments described above, the normal output conditionof the! gate circuit to which the alarm light means were connected was a signal output condition. By placing'the tield contacts in the output circuit in series or parallel" with the red alarm light means, the signal output condition of the' gate did no-t energize the red alarni light means during normaloperation. In the'embodiment now' to be described, the'alarm light means is associated with the gate'circuit which normally does not have a'signal' output condition.` In'the case where normally open`contacts are involved, closure of such contacts will change' the output condition of the gate circuit controlling'the' alarm light means from a no-signal to a signal output condition.- operated, the output conditions of the gate circuits will again be reversed to trigger the controlling gatecircu'it to'a no-signal output condition, thereby extinguishing'the red light associated' therewith. The embodiment' of FIG. 9`uses'the standard plug-inl units 10`and 10 prievi'ously described and, insofar as the left hand gatecircuit'10lis concerned, all connections appearingin thejunction point of the resistor 108 and thel rectifier`106" and a switch 107 which is ganged for operation Withvthel main on-ofi power switch of the annunciator circuitv not Then, when the acknowledgment switchis The terminal shown. The switch 107, in turn, is connected to a source of suitable positive potential 50a, which may be of the same positive potential source utilized throughout the above-mentioned described embodiments of the invention. In this connection, it should also be noted that this power source might either be a source of direct current or pulsating current obtained by rectifying A.C. current. The time constant of the capacitor 110 and the resistor 108 is such that when the switch 107 is closed, a pulse of proper polarity and magnitude will appear across the resistor 108 of suicient duration to inhibit or cancel out the effect of any setting signals fed to the not input terminal 20 of the gate circuit 10 from the output `of the gate circuit Rectifier 106 is so polarized as to pass such pulse generated across the resistor 108.

As soon as the capacitor 1110 charges up to the voltage output of the source 50a, then the pulse disappears from the resistor 108. The inhibit pulse so :fed to the terminal 46 is applied to the bottom end of the input winding 37b of the core unit 37 to inhibit current fioW of the input winding in the same way previously described in connection with the manner in which depression of the acknowledgement switch 8 inhibits current flow in the input winding. As above explained, such inhibit action will initiate a signal output condition at the signal output terminal 18, which signal output condition creates a no-signal output condition at the output of the gate circuit 10, as long as the input circuit to the input winding of the core unit 37 is complete. In the embodiment now being described, the bottom end of the input winding 37b' of the core unit 37 is grounded at all times.

The out-put circuit of `the gate circuit 10' includes the rectifier 52 and the red light R connected to ground. Since, during normal operation of the system, a no-signal output condition exists at the output terminal 18', the red light R will not be energized. The white light W is connected between the positive terminal of voltage source 50 and ground. The negative terminal of the voltage source 50 is connected through a normally open set of condition-responsive field contacts 2 to ground. Thus, as long as the field contacts are open, the white light W will be extinguished.

The positive terminal of the voltage source 50 is connected through an isolating rectifier 1=12 and a capacitor 114 to the terminal 46 of the plug-in unit 10. As pre viously indicated, the terminal 46 is connected to the bottom end of the input winding 37b of the core unit 37. The latter point, in turn, is connected to ground through the input load resistor 43. By a proper proportioning of the capacitor 114 and resistor 43', a suitable time constant will be provided such that even momentary closure of the field contacts 2 will result in the generation of an inhibit pulse across the resistor 43', which is sufficient to inhibit flow of current in the input winding 37b due to the input signals fed thereto from the output of the-gate circuit 10, much in the same way that closure of the power switch 107 provided an inhibit signal which prevented current `flow in the input winding 37b of the core unit 37. Rectifier 112 is polarized to pass a positive voltage pulse arcross the resistor 43 when the field contacts 2 are initially closed, due to an abnormal condition of the variable. This inhibit action, of course, will change the no-signal output condition of the gate circuit 10 to a signal output condition, and due to the feed back loop to the input ofthe gate circuit 1 0, will also result in the changing of the signal output condition of the gate circuit 10 to a no-signal output condition. With the initiation of a signal output condition at the signal output terminal 1S' of the gate circuit 10, the red light R will be energized. Closure of the field contacts 2 will also result in the energization of the white light W.

The output signal of the signal output terminal 18 could, if it had sufficient power capabilities, also operate sti) the common audible alarm 9 connected to the variou. annunciator circuits through respective rectiliers 52.' 52, 52', etc. lf desired, lboth the red and white light and the horn can be controlled through transistor cir cuits analogously arranged like the transistor circuit previously described in connection with FIG. 7.

Upon momentary depression of the acknowledgemen switch 8, an inhibit action occurs at the input of the gati circuit 10 which inverts the output condition of the gatt circuits 10 and 10. Accordingly, the signal output con dition of the gate circuit 10 will be changed to a no signal output condition, thereby extinguishing the rel light R, and the no-signal condit-ion of the gate circui 10 will be converted to a signal output condition, fo reasons obvious from the explanation of the various cir cuits given.

One of the important features of the circuit shown i: FIG. 9 is that the circuit effectively locks-in any initie alarm condition, even though the field contacts immed ately return to their open or normal position. As long a the field contacts are closed for a sufficient time to prt vide inhibit action, the signal output condition of the gat circuit 10 will lbe assured. However, since the field cor tacts 2 are not in the main path of current flow throug the input winding 37b of the core unit 3-7, a reopenin of the field contacts 2 will have no effect on the red ligl R. It Iwill, however, extinguish the white light W. l any rate, even a momentary abnormal operation of th field contacts 2, will be locked in by the continue energization of the red light R, until the acknowledgt ment switch 8 is depressed. In previously described en bodiments, before acknowledgement, as soon as the fiel contacts 2 are in their normal positions, both alarm lights will become extinguished. If the red and whi lights are mounted behind a light-diffusing panel P, z shown in FIG. 6, then a normal lock-in light sequence wi be effected, if a flasher is associated with the red light l FIG. 9, accordingly, shows a suitable flasher 53 connecte in circuit with the red light R.

FIG. 10 gives `the various current and voltage wav forms in the annunciator circuit of FIG. 9, for the variol phases of operation thereof. The waveforms identifie by the reference characters Io-l, Io-l, and Io-1" repr sent the output current pulsations of the gate circuits l respectively during normal, abnormal and acknowledgf operation of the annunciator unit. Similarly, the wav form identified by reference characters Io-Z, Io-2i, ar lo-2 represent the output current of the gate circui 10 respectively during normal, abnormal and acknov edged conditions of operation of the annunciator unit.

FIG. l1 is a chart which gives aresume of conditio. of the core units 37 and 37 with the various symbols t the chart having the same meaning as shown in FIG.

It should -be understood that numerous other modifie tions may be made of the preferred form of the inventii above described, without deviating from the broad aspects of the invention.

As an illustrative but not limiting example, in t broad general aspect of the invention, the magnetic co control circuits of the invention need not have a comm( reference or ground point for the various cascaded ma netic core control circuits, as shown in FIGS. l and 4- and the signal source need not be separate sources ea` having a pair of output terminals, one grounded and t' other not, across which a voltage of opposite phase to t voltage across the output terminals of the other sigr source appear. Rather, the voltage sources, symbolical shown by the numbered circles, could be a single sour with only two output terminals across which an z ternating voltage appears. Each terminal can be said provide an alternating voltage with respect to a theoretir or phantom ground which is opposite to the voltage l tween the opposite terminal and phantom ground. such case, the terminals Z6-32 and 21V-32' of ea plug-in unit 10 or 10' are respectively connected togethc l the joined terminalsl of the plug-in units 10 and 10 connected to opposite terminals of the single two ninal voltage source 50.

n the claims, thel reference to separate main signal rces generally includes the terminals of separate sigsource or the respective terminals of a single source 'ing a phantomv ground, as above explained. Also, the :rence to an input or output terminal does not necesly mean the plug-in unit input or output terminals :rred to, but includes any input or output connection ut` leading to the magnetic core unit' involved.

Ve claim as our invention:

. Anannunciator unit comprising: afirst and a second gne'tic corev not gate circuit, each not gate circuit uding a magneticv core unit with windings thereon, a

n signal input terminal, a not control signal input uinal anda signal output terminal, mainsignal voltage Lns connected to saidmain signalinput terminals of ."rst and second not gate circuits, said first and secmagnetic not gate circuits each further including tris' connecting said various associated terminals to the ciated core windings so that a signal output condition ts where appreciable signalsfrom said signal voltage .ns appear at the associated signal output terminal if a :ignal condition exists at the associated control signal it terminal, anda no-signal output condition exists at associated signal output terminal if an uninhibited al condition exists at the associated not signal input iinal, means connecting said signal output terminal of first not gate circuit to the not input Iterminal of second not gate circuit, wherebyl the output condiof the tirst not gate circuit controls the output lition of said second not gate circuit, means coning said signal output terminal of said second not circuit to the not input terminal of said first not circuit, whereby the output condition of said second gate circuit controls the output condition of said not gate circuit, field switch means'conn'ectedto at one of said no gate circuits for controlling the ut condition thereof and'responsive to the condition variable to be monitored, said field switch means ng opposite'posi-tions indicating respectively anormal an abnormal condition of the variable said not gate lits having a given-initial output condition when said switch means is initially in a normal indicating posivisualv alarm means for providing a normal, an tl abnormal, and an' acknowledged abnormal indicasaid visual alarm means'being connected tosaid iield :h means-and to said signal output -terminal ofV said 1d not gateicircuit, said ieldswitch means, when s normal indicatingr position, operating said visual n means to its normal indicating condition, and, 1 in its'abnormal indicating positionyeffecting the ation of said visual alarm means to its initialab- 1al` indicating condition, acknowledgement switch 1s' vfor selectively providing 'a signal condition at the input terminal yof the not gate circuit which* has gn'al output condition whereby a no-'signal output ition isproduced thereat, said visual alarmmeans beesponsive to said last-mentioned change in the output i'tion-ofsaid latter gate circuit and tothe alarm ining position of-said'rield switch means by providing acknowledged alarm indication, and said field'switch is operating said last mentioned gate circuit to said l V output condition during the operation thereof to )f said positions.

.[An annunciator unitcom'prisin'g1] In'an annuncisystem for monitoring n number of variables, aV first 1 second magnetic core not gatecircuit foreach ble, each not gate circuit including `amagnetic core' with windings thereon', a main signal input terminal, t control signal input terminal and a signal output nal,'main signal voltage means connected tofsaid vsignal inputterminals'of said first and second not ;ircu its, saidrst and second magnetic not gatecirexists at the `associated not signal input terminal, meansr connecting said signal output terminal of said first not gate circuit to the not input terminal of said second not gateV circuit,l whereby the output condition of the tirst not gate circuit controls the output condition of said second not gate circuit, means connecting said sigy nal output terminal of said second not gate; circuit tothe not input terminal of said first not gate circuit, whereby the output condition of said second not gate circuit controls the outputY condition of said rst not gate circuit, ield switch means for euch variable connected to at least one of the associated [said] not gate circuits for controlling the output condition thereof and responsive to the condition of the associated [a] variable to be monitored, eac/1 [said] eld switch means having opposite positions indicating respectively a normal and an abnormal condition of the associated variable, visual alarm means for euch variable for providing a normal,'an initial abnormal, and an acknowledged abnormal indication,` euch [said] Visual alarmV means including [it least one electrical light source [being] connected directly to the associated [said] eld switch meansv andv to said signal: output terminal of' the associated [sai-d] second not gate circuit, each [said]`field switch means, when in its normal indicating position, operating the ussociatedIsaid] visual alarm means including said electrical light source l to its normal indicating condition,fand,when in its abnormal indicating position, effec-ting the operationl of the associated [said] visual alarm means to its initial' abnormal indicating condition by a given output condition of the associated [said] second not gate circuit, said fieldv switch means operating said second notf gate circuit to said given output condition during the operationthereof to one of said indicating positions, acknowledgement switch means for selectively momentarilyv providing a signal condition aty the not input terminal of each [the] not gate circuit having a signal output condition when the associated field switch means is in its alarm indicating position to change said given output condition'of the associatedlfsaid] secondnot gateci-rcuit, to terminate the operation of the associated [said] visual alarm means ink its initial alarm indicating condition, and each [said] eld switehmeans, While in` its alarm indicating-position and subsequent to the operation of said acknowledgement switch means, operating the associated [said] visual alarm means to said acknowledged alarm indicating condition.

3. [An annunciator unit comprisingz] In an annuncialor system for monitoring al number of variables, afirst and a4 second magnetic core not gate circuit for each' variable, each not `gate circuit including a magnetic' core unit with windings, thereon, a main signal input terminal, a not control signal input terminal and a signal output terminal, main signal voltage means connected to said main signal input terminals of said first and second notgate circuits, said firstand second magnetic not gate circuits each further including means connecting said-various associated terminals to the associated' core windings so that -a signal output condition exists where appreciable signals from said'signal voltage means" appear at the associated signal output terminal'if a nosignal condition exists at the associated control signal input terminal, and a no-signal output condition exists at the associated signaloutput terminal if an uninhibited signal condition exists at the associated not signal input terminal, means connecting said signal output terminal of said first not gate circuit to the not input terminal 17 of said second not gate circuit, whereby the output condition of the first not gate circuit controls the output condition of said second not gate circuit, means connecting said signal output terminal of said second not gate circuit to the not input terminal of said first not gate circuit, whereby the output condition of said second not gate circuit controls the output condition of said first not gate circuit, field switch means for each variable connected to at least one of the associated [said] notl gate circuits for controlling the output condition thereof and responsive to the condition of the associated' [a] Variable to be monitored, each [said] field switch means having opposite positions indicating respectively a normal and an abnormal condition of the associated variable, visual alarm light means for each variable for providing a normal, an initial abnormal, and an acknowledged abnormal light indication, each [said] visual alarm means including at least one electrical light source [being] connected directly to the associated [said] field switch means and to said signal output terminal of the associated [said] second not gate circuit, each [said] field switch means,'when in its normal indicating position, operating fthe associated [said] visual alarm means to its normal indicating condition, and, when in its abnormal indicating position, effecting the operation of the associated [said] visual alarm means to its initial abnormal indicating condition by a given output condition of the associated [said] second not gate circuit, said field switch means operating said second not gate circuit to said given output condition during the operation thereof to one of said indicating positions, acknowledgement switch means. for selectively momentarily providing a signal condition at the not input terminal of the associated not gate circuit having a signal output condition when the associated field switch means is in its alarm indicating position to change said given output condition of the associated [said] second not gate circuit, to terminate the operation of the associated [said] visual alarm means in its initial alarm indicating condition, and each [said] field switch means, while in its alarm indicating position and subsequent to the operation of said acknowledgement switch means, operating theV associatekt` [said] visual alarm means to said acknowledged alarm indicating condition.

4. An annunciator unit comprising: a first and a second magnetic core not gate circuit, each no gate circuit including a magnetic core unit with windings thereon, a main signal input terminal, a not control signal input terminal and a signal output terminal, at least said first not gate circuit also having an inhibit control signal yinput terminal, a main signal voltage means connected to said main signal input terminals of said first and second not gate circuits, said first and second magnetic core not gate circuits each further including means connecting said various associated terminals to the associated core windings so that a signal output condition exists where appreciable signals from said signal voltage means appear at the associated signal output terminal if a signal condition exists at both said not and inhibit signal input terminals, and if a no-signal condition exists at both said associated not and inhibit signal input terminals, and a no-signal output condition exists at the associated signal output terminal if a signal condition exists at the associated not signal output terminal and a no-signal condition exists at the associated inhibit signal input terminal, means connecting said signal output terminal of siad first not gate circuit to the not input terminal of said second not gate circuit, whereby the output conditions of the first not gate circuit controls the signal output condition of said second not gate circuit, means connecting said signal output terminal of said second not gate circuit to the notf input terminal of said first not gate circuit, whereby the output condition of said second not gate circuit controlsthe output condition of said first not gate circuit,

field switch means connected to at least one of said not gate circuits for controlling the output condition thereof and responsive to the condition of a variable to be monitored, said field switch means having opposite positions indicating respectively a normal and an abnormal condition of the variable, visual alarm means for providing a normal, an initial abnormal, and an acknowledged abnormal indication, said visual alarm means being connected to said field switch means and to said signal output terminal of said second not gate circuit, said field switch means, when in its normal indicating position, operating said visual alarm means to its normal indicating condition, andwhen in its abnormal indicating position, effecting the operation of said visual alarm means to its initial abnormal indicating condition by a given output condition of said second not gate circuit, said field switch means operating said second not gate circuit to said given output condition during the operation thereof to one of said indicating positions, acknowledgement switch means for selectively providing a signal condition at the inhibit signal input terminal of the not gate circuit having a signal output condition when the field switch means is in its alarm indicating position to change the signal output condition of said second not gate circuit, to terminate the operation of said visual alarm means in its initial alarm indicating condition, and said field switch means, while in its alarm indicating position and subsequent to the operation of said acknowledgement switch means, operating said Visual alarm means to said acknowledged alarm indicating condition.

5. An tannunciator unit comprising: a first and a second magnetic core not Vgate circuit, each not gate circuit including a magnetic core unit with windings thereon, a main signal input termin-al, a "not control signal input terminal and .a signal output terminal, main signal voltage means connected to lsaid main signal input terminals of said rst and second not gate circuits, said first and second magnetic not gate circuits each furthe-r including means connecting said various associated terminals to the associated core windings so that a signal output condition exists where appreciable signals from said signal voltage means 'appear at the associated signal output terminal if a no-signal condition exists at Ithe associated control signal input terminal, and a no-signal output condition exists at the associated signal output terminal if an uninhibited signal condition exists Iat the associated not signal input terminal, means connecting said signal output terminal of said first no gate circuit -to the no input terminal of said second not gate circuit, whereby the output condition of the first not gate circuit controls theoutput condition of said second not gate circuit, means connecting said signal output terminal of said second not"- gate circuit to the not input terminal of said first not gate circuit, whereby the output condition of said second no gate circuit controls the output condition of said first not gate circuit, field switch means connected to at least one of said no gate circuits for controlling the output condition thereof and responsive to the condition of a variable to be monitored, said field switch means having opposite positions indicating respectively -a normal and an abnormal condition of the variable, first visual alarm means for providing at least two different visual indications, second visual `alarm means for providing at least two different visual indications, said field switch means being connected to operate said first visual alarm means independently of said gate circuits to one of its visual indications when said field switch means is in its abnormal indicating position and to its other visual indication when said field switch means is in its normal indicating position, said second visual alarm means being connected to said signal output terminal of said Second not gate circuit, said field switch means in its abnormal indicating position effecting the operation of said second visual alarm means to one of its visual indications by `a given .output condition of. said second -not vgate circuit;

said second visual alarm means having its other visual indication when opposite output condition exists in the output of said second not gate circuit, said field switch means operating said second not gate circuit to said given output condition during the operation thereof to one of said indicating positions, and acknowledgment switch means for triggering said Second not gate circuit to said opposite output condition of said second not gate circuit, to effect the operation of said second visual alarm means to said other visual indication.

6. An annunciator unit comprising: a first and Ia second magnetic core not gate circuit, each not gate circuit including a magnetic core unit with windings' thereon, a main signal input terminal, a not control signal input terminal and a signal output terminal, main signal voltage means connected to said main signal input terminals of said first and second not gate circuits, said first and second magnetic not gate circuits each further including means connecting said various associated terminals to the associated core windings so that a signal output condition exists where appreciable -signals from said signal voltage means appear at the -associated signal output terminal if a nosignal condition exists at the associ- 4ated control signal input terminal, and a no-signal output condition exists at the associated signal output terminal if an uninhibited signal condition exists -at the associated not signal input terminal, means connecting said signal output terminal of said first no gate circuit to the no input terminal of said second not gate circuit, whereby the output condition of the first not gate circuit controls the output condition of said second not gate circuit, means connecting said signal output terminal of said second not lgate circuit to the not input terminal of said first no gate circuit, whereby lthe output condition of said second not gate circuit controls the output condition of said first not gate circuit, field switch means connected to at least one of said not gate circuits for controlling the output condition thereof and responsive to the condition of a variable to be monitored, said field switch means having opposite positions indicating respectively a normal and an abnormal condition of the variable, first Ialarm light means including a first light source for providing -at least two different visual indications, one of which is a bright steady light indication, second alarm light means including a second light source for providing at least two different visual indications, one of which is a bright flashing light indication, said field switch means being connected to operate said first alarm means independently of said gate circuits to its steady bright light indication when said field switch means is in its abnormal indicating position and to its other visual indication when said iield switch lmeans is in its normal indicating position, sad second alarm light means being connected to said signal output terminal of said second not gate circuit, said field -switch means in its abnormal indicating position ef- Ifooting the operation of said second alarm light means to its bright-ashing indication by the output signals from said signal output terminal of said second no .gate circuit, said second alarm light means having its other visual indication when a no-signal condition exists in the output of said -second no gate circuit, acknowledgment switch means for providing a signal condition at the no input terminal of said secondnot gate circuit to cancel the signal output condition of said second no gate circuit, to effect the operation of said second alarm light means lto said other visual indication.

s 7. An annunciator unit comprising: a first and a second magnetic core not gate circuit, each not gate circuit including a magnetic core unit with windings thereon, a main signal input terminal, a not control signal input terminal and a signal output, ter-. minal, main signal voltage means connected to said main signal input terminals of said firsty and second not gate circuits, said mst and second magnetic not gate eadh further including connecting, said various associated to the associated core windings so that a signal output condition exists Where apprcciabie signals rfrom said signal voltage means appear at the associated signal output terminal if a no-signal condition exists at the associated control signal input terminal, and -a no-signal output condition exists at the associated signal output lterminal if an uninhibited signal condition exists at the associated not signal input terminal, means connecting said signal output terminal to said rst not Igate circuit to the not input terminal of said second not gate circuit, whereby ythe output condition of the iirst not gate circuit controls the output condition of said 'second not gate circuit, means connecting said 'signal output terminal of sai-d second not gate circuit to the not inputl terminal of said finst not gate circuit, whereby :the output condition ctt said second not gate circuit controls lthe output condition cf said first not gate circuit, field switch means connected to at least one of said no gate cimcuits for controlling the output condition thereof and responsive tothe condition of a variable to Ibe monitored, said field switch means having opposite positions indicating respectively a normal and an abnormal condition of the variabie, first alarm :light means including a first light source for providing at least two different visual indications, one of which is a bright steady light indication, second alarm light means including a second llight source for providing at least two tdifferent visual in.- fdications, one of which is a bright-dashing indication, a common light diffusing pan-el behind which said iinst and second light sources are mounted so that respective unitary dashing bright and steady lbright indications are provided whenl the 4tvvo light sources are respectively lighted together and when only the nrst llight source is brightly lit, said field switch means being connected to operate said first alarm means independently of said gate circuits to its steady bright light indication when said field switch means is in its abnormal indicating position and to its other visual indication when said 4field switch means is in its normal indicating position, said second alarm light means being connected to said signal output terminal of said second not gate circuit, said field switch means in its abnormal indicating position eiecting the operation orf said second laiarm llight means to its brigllt-ashing indicating 'by la given output condition ccf said second not gate circuit, said second alarm light means having its other visual [indicating] indication when the opposite output condition exists the output of said second "n .gate circuit, said field switch means operating said second no gate circuit 'to said given output condition during the operation thereof to one of said indicating positions and acknowledgement switch means for triggering said second not gate circuit to said opposite output condition to effect the operation of said second alarm light means to said other visual indication.

[8. A n annunciator unit comprising: a first control circuit including first static means having first and second opposite output states, la second control circuit including second static means having first and second opposite output states corresponding respectively fto said first-mentioned output states, means interconnecting said control circuits, so that the two static means have noncorresponding output states at any given condition of the annunciator u nit, wherein changing of the output state of either static means will norm-ally automatically result in a corresponding change in the state of the other static means, means responsive direct-ly to the condition of a variable to he monitored and having a normal and an abnormal condition indicating statte, said condition responsive means setting said static means into a given output state of operation when said variable is normal, visual alarm means having a normal, initial alarm `and acknowledged alarm :states of operation and responsive to at least one change in the output state of one of said static means, said control circuits including means responsive to the change of said condition responsive means from its normal to its abnormal condition indicating state by operating said visual alarm means to said initial alarm state of operation, and responsive to the change of said condition responsive means from its abnormal to its normal state by operating said visual alarm means to its normal state of operation, manually operable acknowledgement means, means responsive to the momentary actuation of said manually operable acknowledgement means for reversing the states of operation of said rst and second static means, and means responsive to the change in the output states of operation of said first and second static means upon operation of said acknowledgement means by operating said visual alarm means to said acknowledged state of operation thero] [9. An -annunciator unit comprising: a first control circuit including first magnetic core means having rst and second output states, a second magnetic core control circuit including second magnetic core means having rst and second opposite output states corresponding respec- Itively to said first-mentioned output states, means interconnecting said control circuits so that the two magnetic cores have non-corresponding output states at any given condi-tion of the fannunciator unit, wherein changing of the output state of either magnetic core will normally automatically resul-t la corresponding change in the output state of the other magnetic core means, condition responsive directly to the condition of a variable to be monitored and having a normal and an abnormal condition indicating state, visual alarm means having a normal, initial alarm and acknowledged alarm states of operation and responsive to at least one change in the output state of one of said magnetic cores, said control circuits each including means responsive to the change of said condition responsive means from its normal to its abnormal condition indioalting state by operating said visual alarm means to said initial alarm state of operation, means responsive to the actuation of said manually operable acknowledgement means -or reversing the states of :operation of said first and second cores, and means responsive to the change in the output states of operation of said nst and second cores upon operation of said acknowledgement means by operating sai-d visual alarm means to said acknowledged state of operation thereof] lv10. [An annunciator unit comprising:] In an annunciator system for monitoring a number of variables, a bistable control circuit for each variable including first static means having iirst and second opposite output states, a second control circuit for each variable including second static means having lirst and second opposite output states corresponding respectively to said first-mentioned output states, means for each variable interconnecting said control circuits so that the two static means have mutually maintained output states, and wherein changing of the output state of either static means will normally automatically result in a corresponding change in the state of the other static means, means for each variable responsive directly to the condition of a variable to be monitored and having a normal and an abnormal condition indicating state, visual alarm means for each variable having a normal, initial alarm `and acknowledged alarm states of operation, and control circuit means for each variable including means responsive to the change of said condition responsive means from its normal to its abnormal condition indicating state by operating the associated [said] visual alarm means to said initial alarm state of operation, manually operable acknowledgement means, means for each variable responsive to the actua'- tion of said manually operable acknowledgement means for reversing the states of operation of the associated [said] first and second static means, and means for each variable responsive to. the change in the output states of .operation of the associated [said] first and second static means upon operation of said acknowledgement means by voperating the associated [said] visual alarm means to said acknowledged state of operation thereof.

[11. An annunciator unit comprising: a first control means including rst static means having iirst and second 'opposite output states, second control means including second static means having first and second opposite output states corresponding respectively to said iirst-mentioned output states, means interconnecting said control means so that the two static means have non-corresponding output states at any given condition of the annunci` ator unit, wherein changing of the output state of either static means will normally automatically result in a corresponding change in the state of the other static means, condition responsive means responsive directly to the condition of a variable to be monitored and having a normal and an abnormal condition indicating state, rst and second Visual alarm means each providing at least twc different visual indications, said condition responsive means when in said normal indicating state operating said first visual alarm means so as to provide a lirst visual indication, and, when in said abnormal indicating state operating said first visual alarm means soI as to provide a second visual indication independently of said control means, said condition responsive means setting one ol said control means into one of its states of operation wher the same is operated between `one of said indicating state: to the other, manually operable acknowledgement means said second alarm means being operated into one of the visual indications when said condition responsive mean: is operated to its abnormal indicating state, means -responsive to the actuation of said acknowledgement meant for 4reversing the output states of said -iirst and seconcv static means, and means responsive to the last-mentionec change in the output states of said iirst and second static means for operating said second visual alarm means fron said one visual indication to another visual indication] [12. An annunciator apparatus comprising yfirst anc second visual alarm means each having de-energized nor mal and energized alarm conditions of operation, a source of voltage, bistable control means comprised of stati( control elements having a first state of operation whicl effects the operation of said second visual alarm mean: to said de-energized normal condition of operation anc a second state of operation which effects the operation o: said second visual alarm means to said energized abnormal condition of operation, condition responsive switcl means responsive to the variable to be monitored anc having normal and abnormal states of operation when th: variable is respectively normal and abnormal, said condi tion responsive switch means when in said abnormal stats of operation connecting said source of voltage into opera tive relation with said first visual alarm means to ener gize the same and effecting the energization of said sec ond visual alarm means by said control means when op eratng in its second state of operation, means for op erating said control means in said second state of opera tion at Ileast during the time said condition responsivr switch means is initially operated to its abnormal statt .of operation, and manually operable acknowledgemen switch means for triggering said bistable control mean` independently of said condition responsive switch mean into said first state of operation thereof where said secon( visual alarm means is de-energized, said bistable contro means being operated into said second state of operatioi when said condition responsive switch means is operate( into one of said states of operation] `13. An annunciatoi unit comprising: a first and a sec `ond not gate circuit, each not gate circuit includin;

a main signal input terminal, a not control signa input terminal and a signal output terminal, main signa voltage means connected to said main signal input ter minals of said first and second not gate circuits, sait first and second no gate circuits each further includ ing means for providing a signal output condition when appreciable signals from said signal voltage means ap pear at the associated signal output terminal if a no-signa condition exists at the associated control signal inpu terminal, and a no-signal output condition at the asso iated signal output terminal if an uninhibited signal Jndition exists at the associated not signal input terlinal, means connecting said signal output terminal of iid first not gate circuit to the no input terminal E said second not gate circuit, whereby the output ondition of the first not gate circuit controls the outut condition of said second not gate circuit, means Jnnecting said signal output terminal of said second not gate circuit to the not input terminal of said first not gato circuit, whereby the output condition of said :cond not gate circuit controls the output condition of tid first not gate circuit, field switch means connected a at least one of said not gate circuits for controlling le output condition thereof and responsive to the conition of a variable to be monitored, said field switch leans having opposite positions indicating respectively normal and an abnormal condition of the variable, first sual alarm means for providing at least two different suai indications, second visual alarm means for providlg at least two different visual indications, said field vitch means being connected to operate said rst visual `arm 4mea-ns independently of said gate circuits to one of s visual indications when said field switch means is in s abnormal indicating position and to its other visual Ldication when said field switch means is in its normal ldicating position, said second visual alarm means being )nnected to said signal output terminal of said second lot gate circuit, said field switch means in its abnormal idicating position effecting the operation of said second .sual alarm means to one of its Visual indications by le output signals from said signal output terminal of said icond not gate circuit, said second visual alarm means iving its other visual indication when a no-signal condian exists in the output Eof said second not gate circuit, :lmowledgement switch means for providing a signal mdition at the not input terminal of said second not tte circuit to cancel the signal output condition of said cond not gate circuit, to effect the ioperation lof said icond visual alarm means to said other visual indication. 14. An annunciator unit comprising: a first and a secld not gate circuit each including a main signal in- 1t terminal, a not control signal input terminal and signal output terminal, main signal voltage means con- :cted to said main signal input terminals of said first ld second not gate circuits, said first 4and second not tte circuits each `further including means for providing signal output condition where appreciable signals from id signal voltage means appear at the associated sigtl output terminal if a no-signal condition exists at the sociated control signal input terminal, and a no-signal itput condition at the associated signal output terminal a signal condition exists at the associated not sigil input terminal, means connecting said signal output rminal of said first not gate circuit to the not put terminal of said second not gate circuit, where- Y the output condition of the first not gate circuit con- :vls the output condition of said second not gate cirlit, means connecting said signal output terminal of id second not gate circuit to the not input terinal of said first not gate circuit, whereby the outlt condition of said second not gate circuit controls e output condition of said first not gate circuit, field litch means connected to at least one of said not tte circuits for controlling the output condition thereof id responsive to the condition of a variable tobe monired, said field Switch means having opposite positions dicating respectively a normal and an abnormal contion of the variable, said field switch means when in L normal indicating position providing a signal output indition at the signal output terminal of said second ot gate circuit, Vfirst visual alarm means for providing least two different visual indications, second visual arm means for providing at least two different visual dications respectively when coupled and uncoupled to e output of said second not gate circuit, said eld switch means being connected to operate said first visual alarm means independently of said gate circuits to one of its visual indications when said field switch means is in its abnormal indicating position and to its other visual indication when said 'field switch means is in its normal indicating position, circuit means connected between said field switch means and said second visual alarm means for coupling the second visual alarm means to the output terminal of said second gate circuit when said field switch means is in its abnormal indicating position and uncoupling the second visual alarm means `from said output of the second gate circuit when the field switch means is in its normal indicating position, and acknowledgment switch means for providing a signal condition at the not input terminal of said second not gate circuit to cancel the signal output condition of said second not gate circuit when said field switch means is in its abnormal indicating position to change the oper-ation of said second visual alarm means.

[15. Annunciator apparatus comprising first and second visual alarm means each operative from a first normal indication to a second alarm indication, condition responsive means responsive to the condition of said variable to be monitored and having a first normal indicating condition when the variable to be monitored is normal and a second abnormal indicating condition when the variable is abnormal, control means for operating said second visual alarm means in its second alarm indication when the control means is in a first state of operation and said condition responsive means is in its abnormal indicating condition and for removing said second alarm indication when the control means is in a second state of operation, said first alarm means being responsive to operation of said condition responsive means to said abnormal indicating condition independently of thestate of operation of said control means, said control means being operated to its first state of operation when the condition responsive means is operated to one of said conditions of operation thereof, and manually operable acknowledgment means for selectively operating said control means independently of the operating condition of said condition responsive means to said second state of operation where the second alarm indication of said second visual alarm means is removed] [16. An annunciator circuit .comprising first and second visual alarm light means each having a de-energized normal condition of operation and an energized alarm condition of operation, operating voltage means for energizing said visual -alarm light means, condition responsive switch means responsive to the lcondition of the variable to `be monitored and having a normal indicating condition when the varia-ble is normal and an abnormal indicating condition when the variable is abnormal, bistable control means comprised of static control elements which effects the energizati-on of said second visual alarm light means when the control means is in a first state of oper-ation and said switch means is in its abnormal indicating position and effects the de-energization of said second visual alarm light means when the control means is in a second state of operation, mean connecting said first visual Aalarm light means, said operating voltage means and said condition responsive switch means into a first circuit whereby the first visual alarm light means will be de-energized when the condition responsive switch means is in its normal indicating condition and is energized when the condition responsive switch means is in its abnormal indicating condition, said rst circuit operating independently of said control means, and means connecting said condition responsive switch means, operating voltage means and said control means in a second circuit where the control means is operated to its lfirst state of operation when the condition responsive switch means is oper- -ated to said abnormal indicating condition thereof, and manually operable acknowledgment switch means for selectively operating said control means to said second 25 state of operation independently of said condition responsive switch means.]

[17. An annunciator circuit comprising rst visual alarm means including a light unit, second visual alarm means including a light unit, -a common translucent panel behind which said light units are mounted to provide an apparently single light indication which is a resultant effect of the two above-mentioned light units, control means for controlling the operation of said second visual alarm means and having two states of operation, said control means in one of said states of operation thereof being adapted alternately to energize and de-energize at la visible dashing rate and in the other state of operation thereof de-energizing the same, condition responsive means for controlling the operation of said first visual alarm means and said control means and having a normal indicating condition when the variable to be monitored is normal and an abnormal indicating condition when the variable is abnormal, means for steadily energizing said rst visual alarm means when said condition responsive means is initially operated to said abnormal indicating condition and rendering said control means operative alternately to energize and de-energize said second visual alarm means whereby an overall flashing indication is provided, one of said conditions of said condition responsivev means operation said control means into said state of operation which is adapted to energize said second visual alarm means, and acknwledgment means for operating said control means to said other state of operation to de-energize the flashing second visual alarm means to provide a steady bright indication from the light unit of said irst visual alarm means if the variable being monitored is still abnormal] 18. An annunciator circuit comprising first normally de-energized visual alarm means including a light unit and adapted to provide a steady bright light indication of said latter light unit when energized, second normally deenergized visual alarm means including a light unit and adapted to provide a dashing light indication on said light unit when energized, a common translucent panel behind which said light units are mounted to provide an apparently single light indication which is a resultant etect of the two above mentioned light units, control means for controlling the operation of at least said second visual alarm means and comprised. of a two stage feedback circuit formed by a pair of static control elements arranged `to have two mutually maintained states of operation and to reverse their respective states of operation when momentarily triggered into an opposite state of operation, said control means in one of said states of operation thereof being adapted to energize said second flashing visual alarm means, and in the other state of operation thereof dfi-energizing the same, condition responsive means for controlling the operation of said control means and having a normal indicating condition when the variable to be monitored is normal and an abnormal indicating condition when the variable is abnormal, means for rendering said control means operative to energize Said second flashing visual alarm means when said condition responsive means is initially operated to its abnormal indicating condition, and acknowledgement means for triggering saidc ontrol means to said other state of operation to de-energize the second flashing alarm means for triggering said control means to said other state state when said condition responsive means is in said abnormal indicating condition and said control means is in said other state of operation to provide an acknowledged alarm indication.

[l9. An annunciator circuit comprising first normally de-energized visual alarm means, a second normally de-energized visual alarm means, control means for controlling the operation of at least said second visual alarm means and comprised of a two stage feedback circuit formed by a pair of static control elements arranged lto have two mutually maintained states of operation and to reverse their respective states of operation when mo mentarily triggered into an opposite state of operation said control means in one of said states of operatioi thereof being adapted to energize said second visual alarn means, and in the other state of operation thereof de energizing the same, condition responsive means for con trolling the operation of said control means and having z normal indicating condition when the variable to b1 monitored is normal and an abnormal indicating conditioi when the variable is abnormal, means for rendering sai control means operative to energize said second visua alarm means when said condition responsive means i initially operated to its abnormal indicating condition, am acknowledgement means for triggering said control mean to said other state of operation to de-energize the secon( visual alarm means, said rst visual alarm means bein; in its energized state when said conditio-n responsivl means is in said abnormal indicating condition and sai( control means is in said other state of operation to pro vide an acknowledged alarm indication] [20. The annunciator circuit of claim l0 wherein sait control circuit means includes means connecting said con dition responsive means to said bistable circuit for operat ing said bistable control circuit into one of its states o operation in response to the change of said condition re sponsive means from its normal to its abnormal indicat ing state, and means responsive to the operation of sait bistable control circuit to said one state of operation fo effecting the operation of said visual alarm means to sait initial alarm state of operation] [21. The annunciator of claim l0 including means con necting said condition responsive means into said bistabli circuit for operating the same into a predetermined initia state of operation when the condition responsive means i operated to its normal indicating state] [22. The annunciator circuit of claim l() wherein then is provided means automatically responsive to the initia energization of the annunciator circuit -for setting the bi sta-ble circuit into a predetermined initial state of opera tion] [23. The annunciator circuit of claim l0 wherein theri is provided means for initially setting said bistable -circui into a predetermined initial state of operation] 24. The annunciator circuit of claim l0 wherein eac) of said static means are magnetic core gate units.

25. An annunciator unit comprising: u first alud o sec ond mugmetic core not gate circuit, each not gurl circuit including u magnetic core unit with winding thereon, a main` signal input terminal, d not contro signal input terminal and a signal output terminal, mail signal voltage means connected to said main signal inpu terminals of said first and second not gate circuits, sait first und second magnetic no gate circuits euch fur ther including means connecting said various associutet terminals to the lassociated' cone windings so that a sig nul output condition exists where appreciable signal from said signal voltage means appear at the associato signal output terminal if a ufo-signal condition exists a the associated control signal input terminal, und al no signal output condition exists at the associated signa output terminal if on uninhibited signal condition exist at the associated not signal input terminal, means con necting Suid signal output terminal of said first not gute circuit to the not input terminal of said secom not gute circuit, whereby the output condition of thl first "nof gute circuit controls the output condition o said second not gate circuit, means connecting suit signal output terminal of said second not gate circui to the not input terminal of said first not gutev cir cuit, whereby the output condition of said second not gute circuit controls the output condition of said firs "not gate circuit, condition responsive means havin,l normal und abnormal indicating conditions when; the as sociated variable is respectively normal and abnormal meuns connecting said condition responsive means to om F said magnetic core "not gate circuits to inhibit the lect of any signals on the "not control signal input lrminal for the period during which a condition responve means is in said normal indicating condition, and rereby provide a signal output condition on the associed not gate circuit, and a no-signal output condition i the other not gate circuit, visual alarm means for oviding a normal, initial abnormal, and an acknowllged abnormal indication, said visual alarm means beg responsivfe to the signal output conditon of said firstentioned not gate circuit and to the abnormal condi- ?n of said condition responsive means for providing an itial abnormal indication, acknowledgment switch eans for reversing the signal output states of said "not" ite circuits when the condition responsive means is in s' abnormal condition, and said visual alarm means beg responsive to said reversal of the signal output condi- ?ns of said not gate circuits by the operation of said anually operable acknowledgment means for providing 'id acknowledged abnormal indication, field switch eans connected tol at least one of said not gate ciriits for controlling the output condition thereo]c and sponsive to the condition of a variable to be monifred, said field switch means having opposite positions dicating respectively a normal and an abnormal condi- 7n of the variable said not gate circuits having a given itial output condition when said field switch means is itially in a normal indicating position, visual alarm eans for providing a normal, an initial abnormal, and i acknowledged abnormal indication, said visual alarm means being connected to said field switch means and to said signal output terminal of said second not gate circuit, said field switch means, when in its normal indicating position, operating said visual alarm means to its normal indicating condition, and, when in its abnormal indicating position, effecting the operation of said visual alarm means to its initial abnormal indicating condition, acknowledgment switch means for selectively providing a signal condition at the not input terminal of the not gate circuit which has a signal output condition whereby a no-signal output condition is produced thereat, said visual alarm means being responsive to said last'- mentioned change in the output condition of said latter gate circuit and to the alarm` indicating position of said field switch means by providing said acknowledged alarm indication, and said field switch means operating said last-mentioned gate circuit to said signal output condition during the operation thereojc to one of said positions.

References Cited in the e of this patent or the original patent UNITED STATES PATENTS 

